This invention relates to radar systems and more particularly to time compressed display of radar video signals.
In any time compressed display, signals or data which has been accumulated over a long period of time may be presented to the operator in a very short time span, for instance, at T.V. frame rates. FIG. 1 is a block diagram of a conventional prior art design used for a time compressed radar display. Referring now to FIG. 1 this prior art technique will be described. Typically, incoming radar video data in the form of analog signals is converted to digital signals via analog-to-digital converter 12. Incoming radar position data is converted from its polar coordinate format by scan converter 14 to a rectangular coordinate format which is T.V. compatible. Every time the radar scanning antenna completes a revolution, the entire radar video history for that scan is stored on a T.V. video disc or some other bulk storage medium 16. The entire video history for each scan is thus stored. A write frame counter 18 is incremented once each antenna revolution by the antenna once around network 20 and is used to generate an address to put the frame of data in storage. For storing 16 frames of incoming video information, for instance, a four-bit write frame counter would be used. The write frame counter is typically a modulo counter which in real time is counted from 0 to 15 (in the present example) over and over again. At the end of each antenna scan the video return for that scan is used to replace the previously stored frame with the current frame of data for the most recent scan. This allows the video disc bulk storage area to always contain the video returns for the most recent 16 scans (in the present example) of the antenna. At the output, the read frame counter 22 is used to address the frames in bulk storage 16 in chronological order, i.e. the order in which they were recorded. The reading from the bulk storage area 16 is typically done at 525 line T.V. rates with the read frame counter 22 being incremented once per T.V. frame time. This is done under control of the timing and control network 24. The data is read out of the bulky memory 16 via T.V. formatter 26 to a T.V. display. An operator looking at the display sees the history of the last 16 (in the present example) antenna scans presented to him over and over again at T.V. frame rates. This presentation allows the operator to readily detect moving targets on the screen through the clutter.
The problem with this approach is that there is a significant degree of frame-to-frame redundancy and the bulk memory requirements are enormous.